Vacuum tube filament structure



Dec. 5, 1933. UTHERLlN 1,937,856

VACUUM TUBE FILAMENT STRUCTURE Filed Nov. 10.. 1922 Fig. 1.

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i f BY flag ATTORNEY Patented Dec. 1933 PATENT OFFICE 1,937,856 I VACUUM TUBE FILAMENT STRUCTURE Lee Sutherlin, East Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application November 10, 1922 Serial No. 599,984

15 Claims. (o1. 250-275) My invention relates to evacuated electric devices, having particular relation to, the cathode structure of such devices.

One object of my invention is to provide a vacuum-tube device embodying a filament construction wherein the filament is excited from alternating-current sources of energy without the introduction of the usual so-called alternating-current hum in the operation of the device.

Another objectof myinvention is to provide a cathode structure embodying such design as to avoid the usual microphonic action hereinbefore observed in most vacuum-tube devices.

A further object of my invention is to provide 5 a cathode structure which is characterized by its rigidity of construction and efiiciencyof operation and by the absence of adjusting springs heretofore employed to compensate for the expansion and contraction of the filament. Heretofore, considerable difiiculty has been experienced inthe excitation of the cathode element of detecting and amplifying vacuum tubes ofthe threeelectrode type by alternating currents of commercial :frequency because of the periodic variation inthe voltage-current characteristic of the tube, resulting in the so-called alternatingcurrent hum in telephone devices associated therewith. V

Aiurther disadvantage of many types of vacuum tubes heretofore employed consists in the microphonic action observed in the operation of the tube when the same is jarred. Such microphonic action may take the form of a sustained note of several minute duration and may be detectedin thetelephone receivers associated with the plate-filament elements of the tube. I'have found that the difiiculties heretofore encountered in the excitation of vacuum-tube filaments by alternating currents of commercial fre- 40 quency is mainly caused by the variations in the intensity of the magnetic field established by the exciting currents traversing the filament. I have further observed that the microphonic action is materially decreasedby providing a loose support 5 for the'filament rather than a resilient support,

as has heretofore been the custom.

In practicing my invention, I provide a vacuum-tube, device having a filament structure wherein the filament element may expand and contract without serious distortion, wherein the filament is so supported as to eliminate the microphonic action previously mentioned and wherein the disturbing efiects of the periodic variations in the intensityof the filament-current magnetic g 95 fields are substantially. avoided.

With these and other objects and applications in view, my invention further consists in the nature, the mode of operation and the constructional details hereinafter described and claimed and illustrated in the accompanying drawing, 30

wherein,

Figure 1 is an enlarged iront-elevational view of an evacuated electrical device embodying my invention, a portion of the containing walls being broken away and the anode and grid elements being shown-in longitudinal section, a

Fig. 2 is a front-elevational detailed view of the cathode structure shown in Fig. 1, and

Fig. 3 is a side-elevational view of the apparatus of Fig.2. V

In one embodiment of my invention, I provide an evacuated electrical device comprising an 61011.- gated tube 1 having a re-entrant portion 2 at one end thereof terminating in a supporting press 3.

By way of illustration, a cylindrical anode 4 is positioned in the tube 1 co-axial with the longitudinal axis thereof, the same being supported by. carrier rods 5 and 6 extending from the supporting press 3. One carrier rod, say 6, may be extended through the press 3 to provide an external terminal connection for the anode 4.

A grid '7 of helical shape is co-axially positioned within the space inclosed by the anode 4 and is supported by means of a carrier rod'8 which extends from the press 3 and engages the helices of the grid '7. The carrier rod 8 may be extended through the press 3 to provide an external connection for the grid 7. y

A filament 9 is constructedin the form of a U and comprises a bent portion 11 and parallel-extending bent-back portions .12 and 13. The filament 9 is positioned in the common 1ongitudinal axis of the grid 7 and of the, anode 4 and has itsterminals secured to supply rods 14 and 15 extending from the press 3. The supply rods 14 and 15 may be extended through the press 3 to provide external terminal connections for the filament 9. r The two sections or bent-back portions 12 and 13 of the filamentQ are positioned with a minimum space therebetween in order that the magnetic field established by currents in the one section may substantially neutralize the magnetic field established by currents in the other section, thereby providing a filament which lendsitself to excitation by alternating currents without the usual variations in the voltage-current characteristic of the device. The sections 12 and 13 may be insulatingly separated by a flat strip 16 of mica or other insulating material having a small groove or indentation 17 at one end engaging the bent portion 11 of the filament 9.

The filament 9 may or may not be made to adhere to the insulating strip 16, depending upon the particular means employed for imparting rigidity and ruggedness to the filament support as a whole. If the filament 9 is of the so-called ribbon type, the fiat sides of the filament sections are placed next to the insulating strip 11 in order to make the average distance between the filament sections or branches as small as possible. The insulating member 16, which has been shown in the drawing in the form of a mica strip, may be supported independently of the means for supporting the filament, or the insulating material may be supported and then used as a filament support. g

In the drawing is shown one arrangement wherein the insulating material 16 serves as a support for the filament 9, in addition to insulatingly separating the branches 12 and 13 of the filament. The desired result is accomplished by providing the end of the insulating strip 16 adjacent to the bent portion 11 of the filament 9 with oppositely extending arms 18 and 19 which engage the unsupported end of the anode i. In such construction, the filament 9 is supported at a'single point where the indented portion of the insulating strip 16 engages the bent portion 11 of the filament 9. The filament 9, however, is preferably supported on the filament-supporting member 16 in a fairly loose condition, thereby minimizing the microphonic noises characteristic of the usual type of vacuum-tube construction.

While I have described, in detail, a certain specific embodiment of my invention, and while I have pointed out certain of the most obvious principles thereof, I do not intend that the language employed in the appended claims shall be limited to the precise features described, but I intend that the claims shall be construed to cover all combinations which are fairly included in the language thereof, when read in connection with the prior art, regardless of the details and functions mentioned in the description or illustrated in the drawing. I

I claim as my invention: 7

1. In combination, an insulating support having opposite faces, and a cathode element having parallel extending sections carried by said support each of said opposite faces having one of said parallel sections disposed adjacent thereto.

2. A cathode structure for a thermionic device including a filament, comprising successive parallel sections serially connected, a filament support comprising a longitudinally extending portion insulatingly separating the individual sections of said filament, said support having laterally extending portions forming supporting arms.

3. A cathode structure for a vacuum tube comprising a filament, a thin insulating member having a longitudinally extending portion and a pair of laterally extending arms, said member being indented at one edge, said filament passing extending portion symmetrically disposed with respect to said anode and also having laterally extending portions engagin' said anode, said anode constituting a support for said member, and a filamentary element carried by said memher.

5. A spacewurrent device comprising an envelope enclosing an anode, a filamentary cathode having adjacently disposed sections and a bent portion connecting them, and an insulating member separating said cathode, said insulating memer having an end portion engaging said cathode at the bent portion thereof, and arms extending from said insulating member and engaging said anode, whereby said filamentary cathode is supported by said anode.

6. A space-current device comprising an envelope enclosing a cylindrical anode, a longitudinally extending member having opposite faces, integral extensions from said member positioning the member substantially in the axis of said anode, and a filament carried by said member and having portions disposed adjacent to said opposite faces.

7. A space-discharge device comprising an envelope enclosing a cylindrical anode having opposite ends, a filament having two successive parallel sections disposed in the longitudinal axis of said anode, insulating means for maintaining said sections in such spaced relation that the magnetic field established by currents traversing one section substantially neutralize that established by the currents traversing the other section, and integral extensions from said insulating means for engaging one end of said anode, whereby said filament may be supported.

3. A space-discharge device comprising an envelope enclosing a cylinder-like anode having opposite ends, a filament having two successive, parallel sections disposed in the longitudinal axis of said anode, a strip of mica interposed between said sections for insulatingly spacing the sections in such manner that the magnetic fields established by currents traversing the sections balance, and integral-extensions from said strip for engaging said anode, whereby said filament is insulatingly supported.

9. A vacuum tube enclosing a cylindrical anode, a sheet of insulating material having a longitudinally extending portion and a transversely extending portion and having its longitudinal member within the anode and its lateral members resting on the top of the anode and a filament supported by said sheet of insulating material.

10. A vacuum tube enclosing a cylindrical anode, a sheet of insulating material having a longitudinally extending portion and a transversely extending portion and having its longitudinal member within the anode and its lateral members resting on the top of the anode, and a filament mainly within said anode and extending across the top of said member.

11. A cathode structure comprising a filament support, a non-inductive filament rigidly carried thereby and closely adjacent thereto whereby heat interchange may occur between said filament and its support.

12. A. vacuum tube enclosing a plurality of electrodes including a substantially non-inductive filament therein, an insulating body non-microphonically supporting said filament and means for applying alternating current for heating said filament whereby the insulating body will receive heat from said filament.

13. A vacuum tube'enclosing a plurality of electhe filament and the body of the support being so close that the interchange of heat between the filament and the support will tend to obliterate the variations in electron emission arising from the periodic character of the heating current.

15. A cathode structure for a vacuum-tube de-- vice comprising a sheet of mica, a U-shaped filament having its arms closely adjacent to the faces of the mica and non-microphonically supported thereby.

LEE SUTHERLIN. 

